As known well, a contact type IC card is coupled to through a contact point to an external device, e.g., a data reader/writer (simply “reader/writer” hereinafter), and performs the transmission and reception of signals between it and the reader/writer while being supplied with electric power through the contact point. On the other hand, a non-contact IC card is coupled to the reader/writer in a non-contact state through an antenna and performs the transmission and reception of signals between it and the reader/writer while being supplied with electric power through the antenna.
Recently, a single card which can operated in either the above contact or non-contact states has been devised or being developed as a dual interface IC card (see, for example, Published Japanese Translations of PCT International Publication for Patent Applications No. Hei 10-505932). The dual interface IC card is convenient for users and therefore its application range is being widened.
FIG. 4 shows the configuration of an internal circuit 12 in a conventional dual interface IC card. The internal circuit 12 is integrated into an IC chip. In case of operation in a non-contact state, electric power and signals are supplied through a coiled antenna 1, while in case of operation in a contact coupling state, electric power and signals are supplied through a contact point 2. As bidirectional signals to and from an information processor 3, signals having gone through either the antenna 1 or the contact point 2 are selected by a selector 4. For example, in the prior art being considered, the selection is made by detecting that electric power has been fed to a terminal Vdd of the contact point 2, which detection is performed by a voltage detector 11. As a result of the detection, the signals having gone through the contact point 2 are selected.
Usually, the information processor 3 has a processing unit and a memory and reads the contents of the memory in accordance with directions given by a reader/writer and provides a transmission signal or rewrites the memory contents in accordance with a reception signal provided from the reader/writer.
In a non-contact operation, electric power is obtained by rectifying a high frequency signal received by the antenna 1 in a rectifier 5, smoothing the rectified signal in a capacitor C and making the voltage thereof into a predetermined voltage in a series regulator 6. On the other hand, electric power from the contact point 2 is obtained directly from the reader/writer through the terminal Vdd.